Ceramic honeycomb structural body and method of manufacturing the structural body

ABSTRACT

The ceramic honeycomb structure according to the present invention includes a cell group having a plurality of cells which are divided each other by porous partition walls and functioning as a fluid channel, and porous outer wall surrounding and holding outermost peripheral cells located at a circumference of the cell group. In the partition walls, a part located at least one opening end of the cells of the cell group constitutes a reinforced partition wall part having higher strength than the other part of the partition walls (normal partition wall part) as well as having a variation of porosity per unit volume within ±2%. Uniform and excellent erosion resistance is achieved throughout the reinforced partition wall part.

TECHNICAL FIELD

The present invention relates to a ceramic honeycomb structure and amethod of producing the same, and more specifically to a ceramichoneycomb structure which is suited for a carrier for controllingexhaust gas emission of automobile, ensuring a good balance betweenemission control performance and durability and canning property of endface, and a method of producing the same.

BACKGROUND ART

In ceramic honeycomb structural bodies widely used as a catalyst carrierand the like for emission control of exhaust gas, there is an increasedneed for improved emission control performance in order to comply withthe emission regulations that have been tightened year by year, whilereducing the pressure loss for satisfying the requests for fuel economyand high output.

In such circumstances, the growing trend is to increase the porosity atan opening end of cells of the honeycomb structure by further reducingthe thickness of partition walls of the honeycomb structure, therebyreducing the pressure loss, as well as to increase the emission controlperformance by ensuring immediate activation of the catalyst afterstartup of the engine by reducing the heat capacity of the partitionwalls.

On the other hand, the development of such honeycomb structure havingthinner walls raised the new problem that a variety of contaminantshaving entered the exhaust gas collide with the partition walls locatedat opening ends of cells of the honeycomb structure to damage thepartition wall. This phenomenon is known as a erosion phenomenon.

To address this problem, already proposed is a honeycomb structurewherein a partition wall reinforcing part (reinforced partition wallpart) having higher strength than the remaining part of the partitionwalls is provided in partition walls located at an opening end of cells(See Patent document 1, for example), and in this proposal, the mannerof providing the partition wall reinforcing part is widely studied.

One conventionally known method of providing a partition wallreinforcing part includes the steps of: firing a base material having ahoneycomb structure based on a cordierite forming raw material; adheringa slurry in which a cordierite forming raw material is dispersed in adispersing medium, to the partition walls located at an opening end ofcells of the base material; and drying and firing the resultant basematerial (See Patent document 1, for example).

However, in this method, the time-consuming firing process must beconducted twice, namely, firing of the base material and firing forproviding the partition wall reinforcing part, so that there is still agreat problem regarding the production efficiency, product cost and thelike.

To address this problem, also suggested is a method in which a slurryprepared by dispersing a partition wall reinforcing material in adispersing medium is caused to adhere to the partition walls located atan opening end of the cells before the base material having a honeycombstructure is fired, and then drying and firing were conducted. Thismethod accomplishes firing of the base material and formation of thepartition wall reinforcing part by a single firing step (See Patentdocument 1, for example).

However, as to this method, no substantial study about the difference ina material composition between the base material before firing and thebase material after firing has been made at the moment. In particular,the base material before firing usually contains an organic binder orthe like added for the purpose of, for example, improving the strengthof the partition walls, however, no consideration was made on the factthat the organic binder is often a water-soluble compound such as methylcellulose.

For this reason, if the step of forming a partition wall reinforcingpart that is conventionally conducted after the firing step is carriedout as it is before firing using a slurry prepared by dispersing thepartition wall reinforcing material in water, the organic binderliquates out in the slurry to cause deformation in the partition wallsand the like of the obtained honeycomb structure, making it unendurableto practical use due to reduction of isostatic strength or the like.

Additionally, in the case of the slurry prepared by dispersing apartition wall reinforcing material in a dispersing medium, dispersivityof the partition wall reinforcing material is likely to be insufficientbecause of sedimentation or aggregation of the partition wallreinforcing material caused by its physical property. This often resultsin variation or unevenness in the partition wall reinforcing part indegree of reinforcement. Accordingly, this production method suffersfrom the problem of impossibility to reliably obtain a ceramic honeycombstructure having uniform erosion resistance throughout the partitionwall reinforcing part or the problem of increase in management burdenfor uniformly dispersing the partition wall reinforcing material.

To the contrary, the problem such as decrease in isostatic strength dueto deformation of the partition wall or the like can be overcome byusing a slurry prepared by dispersing the partition wall reinforcingmaterial in a non-aqueous dispersing medium.

However, the problem of impossibility to reliably obtain a ceramichoneycomb structure having uniform erosion resistance throughout thepartition wall reinforcing part or the problem of increase in managementburden for uniformly dispersing the partition wall reinforcing materialis not solved at all in this production method.

(Patent Document 1)

Japanese Unexamined Patent Publication JP-A 2000-51710

The present invention was devised in consideration of the above problemsof the prior art, and it is an object of the invention to provide aceramic honeycomb structure having uniform and excellent erosionresistance throughout the reinforced partition wall part, and a methodof producing a ceramic honeycomb structure capable of obtaining ahoneycomb structure having desired performance without causingdeformation or the like in the partition walls while dramaticallyimproving the productivity and the product cost, as well as forming asophisticated and uniform reinforced partition wall part with highaccuracy.

DISCLOSURE OF THE PRESENT INVENTION

The inventors of the present invention have diligently studiedconsidering the aforementioned problems, and found that by using as apartition wall reinforcing agent, a material based on a compound havingat least one kind of atom selected from the group consisting of Si, Ti,Mg and Al in its structure, such as silicone oil, the aforementionedproblems can be solved, which accomplished the present invention.

That is, according to the present invention, there is provided a ceramichoneycomb structure comprising: a cell group having cells, the cellsbeing divided each other by porous partition walls and functioning as afluid channel; and a porous outer wall surrounding and holding outermostperipheral cells located at a circumference of the cell group, whereinin the partition walls, a part located at least one opening end of thecells of the cell group is a reinforced partition wall part havinghigher strength than the other part of the partition walls as well ashaving a variation of a porosity per unit volume within ±2%.

In the present invention, it is preferred that the value of porosity (%)of the reinforced partition wall part is smaller than the value ofporosity (%) of the normal partition wall part by 3 (%) or more. In thepresent invention, it is preferred that the porosity of the reinforcedpartition wall part is not more than 30%.

In the present invention, preferably, the minimum wall thickness of thepartition walls is in the range of 0.030 to 0.076 mm, and the lengthfrom the end face of the opening end of the cells to the tip end of thereinforced partition wall part is not uniform throughout the reinforcedpartition wall part.

In the present invention, it is preferred that the thickness of thepartition walls of the reinforced partition wall part is larger than thethickness of the partition walls of the normal partition wall part.

In the present invention, taking the outermost peripheral cell as astarting cell, taking any cell of the third to the twentieth celllocated inwardly from the starting cell as an end cell and taking cellslocated inwardly from the end cell as basic cells, it is preferred thata relation between thickness (Tc) of partition walls forming the basiccells and each thickness (Tr1, Tr3-20) of partition walls forming thestarting cell and the end cell is 1.10≦(Tr1, Tr3-20)/Tc≦3.00.

In the present invention, the ceramic honeycomb structure is preferablyformed of at least one kind of ceramic selected from the groupconsisting of cordierite, alumina, mullite, silicon nitride, aluminumtitanate, zirconia and silicon carbide.

In the present invention, a sectional shape of the honeycomb structureperpendicular to the channel is preferably circular, elliptic, oval,trapezoidal, triangular, tetragonal, hexagonal or asymmetric, and asectional shape of the cell perpendicular to the channel is preferablytriangular, tetragonal or hexagonal.

The ceramic honeycomb structure of the present invention is preferablyused as a carrier for catalyst for purification of automobile exhaustgas. It is also preferred that a catalyst component is loaded on thepartition walls of the honeycomb structure, which is assembled into acatalytic converter, and held at the outer surface of the outer wall.

Furthermore, according to the present invention, there is provided amethod of producing a ceramic honeycomb structure including the steps ofobtaining a base material which is a dry body of honeycomb structurehaving a plurality of partition walls using a kneaded compound based ona ceramic material, adhering a partition wall reinforcing agent to thepart of the partition walls located at least one of the opening ends ofthe cells in the base material, and firing the resultant base material,wherein as the partition wall reinforcing agent, a material based on acompound having at least one kind of atom selected from the groupconsisting of Si, Ti, Mg and Al in its structure is used.

In the present invention, the partition wall reinforcing agent ispreferably based on a compound generating an inorganic oxide uponfiring, and more preferably a compound having a siloxane bond. To bemore specific, a partition wall reinforcing agent based on silicone oil,silicone varnish, alkoxy oligomer or a mixture thereof is preferred.

Preferably, the partition wall reinforcing agent has an absoluteviscosity of 1 to 10000 mPa·s and is based on a compound having such anabsolute viscosity.

In the present invention, a variety of materials can be used as aceramic material, and it is preferred to select the kind of thepartition wall reinforcing agent in accordance with the kind of theceramic material. For example, when a cordierite forming raw material isused, compounds having Si in their structures such as silicone oil arepreferred.

Furthermore, in the present invention, when a water-soluble organicbinder is contained in the kneaded compound in addition to the ceramicmaterial which is the basis, the effect thereof is especially large.Concrete examples of the water-soluble organic binder include thosecomprising at least one kind of water-soluble compound selected from thegroup consisting of hydroxypropylmethyl cellulose, methylcellulose,hydroxyethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol andpolyvinyl acetal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing the region sampled for determiningPorosity 1 (product-to-product difference) for ceramic honeycombstructural bodies according to each Examples and each ComparativeExamples.

FIG. 2 is a schematic view showing the region sampled for determiningPorosity 2 (uniformity of reinforced partition wall part) for ceramichoneycomb structural bodies according to each Examples and eachComparative Examples.

FIG. 3 is an enlarged view showing a condition of a part of thepartition walls in the ceramic honeycomb structure obtained by theproduction method of Example 1.

FIG. 4 is an enlarged view showing a condition of a part of thepartition walls in the ceramic honeycomb structure obtained by theproduction method of Comparative Example 2.

FIG. 5 are explanatory views schematically showing an embodiment of theceramic honeycomb structure of the present invention. FIG. 5(a) is aperspective view, FIG. 5(b) is a plane view and FIG. 5(c) is a sideview.

FIG. 6 is a partially enlarged view schematically showing anotherembodiment of the present invention.

FIG. 7 is an explanatory view schematically showing an example in whichthe ceramic honeycomb structure of the present invention is incorporatedinto a converter container.

FIG. 8 is a view showing the condition of the engine revolutions in theerosion test.

FIG. 9 is an explanatory view schematically showing a method ofdetermining an erosion amount.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described below more specifically.However, the present invention is in no way restricted to theembodiments described below. The ceramic honeycomb structure accordingto the present invention is a ceramic honeycomb structure comprising acell group consisting of a plurality of cells which are divided eachother by porous partition walls and functions as a fluid channel and aporous outer wall surrounding and holding outermost peripheral cellslocated at a circumference of the cell group, wherein in the partitionwalls, a part located at least one opening end of the cells of the cellgroup is a reinforced partition wall part having higher strength thanthe part other than the part located at least one opening end of thecells (hereinafter, referred to as “normal partition wall part”) as wellas having a variation of a porosity per unit volume (hereinafter,referred to as “maximum difference in porosity”) within ±2%. Next,detailed explanation thereof will be provided.

FIG. 5 are explanatory views schematically showing an embodiment of theceramic honeycomb structure of the present invention. FIG. 5(a) is aperspective view, FIG. 5(b) is a plane view and FIG. 5(c) is a sideview. FIG. 6 is a partially enlarged view schematically showing anotherembodiment of the present invention. A ceramic honeycomb structure 1 hasa cell group consisting of a plurality of cells 3 which are divided eachother by a plurality of porous partition walls (cell partition walls 2)and functioning as a fluid channel and a porous outer wall 4 surroundingand holding outermost peripheral cells 8 located at a circumference ofthe cell group. In FIG. 6, the reference numeral 2 a represents aperipheral cell partition wall, the reference numeral 2 b represents abasic cell partition wall and the reference numeral 9 represents asecond cell from the circumference of the cells.

In the ceramic honeycomb structure 1 according to the embodiment shownin FIG. 5, in the partition walls (cell partition walls 2), a partlocated at least one opening end 5 of the cells of the cell groupconstitutes a reinforced partition wall part having higher strength thanthe normal partition wall part. Therefore, the ceramic honeycombstructure 1 according to the present invention has excellent erosionresistance.

The maximum difference in porosity of the reinforced partition wall partis within ±2%, in other words, high uniformity is achieved. Therefore,in the ceramic honeycomb structure 1 of the present embodiment,variation in chance of occurrence of erosion depending on the region ofthe reinforced partition wall part is very small, so that occurrence oflocal erosion phenomenon can be avoided. Accordingly, excellent erosionresistance is realized throughout the reinforced partition wall part.

In the ceramic honeycomb structure according to the present embodiment,the maximum difference in porosity among five regions of the reinforcedpartition wall part is preferably within ±1.5%, more preferably within±1% from the view point of giving more excellent erosion resistance. Inthis context, the phrase “maximum difference in porosity of thereinforced partition wall part” concretely means a variation of porosityper unit volume among any five regions within the reinforced partitionwall part.

In the present embodiment, the value of porosity (%) of the reinforcedpartition wall part is smaller than the value of porosity (%) of thenormal partition wall part preferably by 3(%) or more, more preferablyby 5(%) or more, and especially preferably by 8(%) or more. If the valueof porosity (%) of the reinforced partition wall part is smaller thanthe value of porosity (%) of the normal partition wall part by less than3(%), such case is unfavorable because sufficient erosion resistance isdifficult to be exerted. Although the upper limit of the value by whichthe value of porosity (%) of the reinforced partition wall part issmaller than the value of porosity (%) of the normal partition wall partis not particularly restricted, but it should be generally 12(%) orless.

In the present embodiment, the porosity of the reinforced partition wallpart is preferably not more than 30%, more preferably in the range of13% to 25%, still preferably in the range of 15% to 23%, and mostpreferably in the range of 18% to 21% from the view point of achievingboth the thermal shock resistance and the erosion resistance.

In the present embodiment, the minimum wall thickness of the partitionwalls is preferably in the range of 0.030 mm to 0.076 mm, and morepreferably in the range of 0.030 mm to 0.065 mm. By defining the minimumwall thickness in such a range of value, it is possible to improve theemission control performance during warm-up by reducing the weight andheat capacity while reducing the pressure loss.

From the view point of achieving both the erosion resistance and smallheat capacity, the reinforced partition wall part is disposed in a partor the whole of the range within 30 mm, more preferably within 10 mm inthe axial direction from at least one end face of the opening end of thecells. Furthermore, in the ceramic honeycomb structure of the presentembodiment, the reinforced partition wall parts may extend the sameaxial length from the end face of the opening end of the cells, however,it is preferred that the length from the end face of the opening end ofthe cells to the tip end of each reinforced partition wall part is notequal throughout the reinforced partition wall part, from the view pointof achieving both the erosion resistance and small heat capacity, andrestraining stress concentration at the boundary where the porositychanges.

In the present embodiment, it is preferred that the wall thickness ofthe reinforced partition wall part is larger than the wall thickness ofthe normal partition wall part. More specifically, the wall thickness ofthe reinforced partition wall part is preferably 1.20 to 4.00 times thewall thickness of the normal partition wall part. Also it is preferredfrom the view point of avoiding stress concentration that the wallthickness of the reinforced partition wall part decreases sequentiallyor stepwise in the axial direction from at least one end face of theopening end of the cells to transit to the wall thickness of the normalpartition wall part. Various kinds of reinforced partition wall partsmay be used singly or in combination of two or more kinds.

In the present invention, it is also preferable for improvement oferosion resistance that the cell walls 2 a near the circumference of thehoneycomb structure are made thick as shown in FIG. 6. By making thecell walls 2 a near the circumference thick, it is also possible toimprove isostatic strength as well as to increase holding strength incanning. Therefore, canning property can be improved. Here, “isostaticstrength” is a strength obtained by a test conducted based on anautomobile standard JASO M 505-87, and expressed by an applied pressurewhen breakage occurs. In FIG. 6, there are outermost peripheral cells 8closest to the outer wall 4, and second cells 9 extend inwardly from theoutermost peripheral cells 8. The wall thickness of the outermostperipheral cells is indicated by Tr1 and the wall thickness of thesecond cell 9 is indicated by Tr2. Any cell (not shown) of fifth tofifteenth cells is indicated by Tr5-15. Incidentally, cell walls 2 arelargely divided into cell walls 2 a near the circumference and basiccell walls 2 b.

In the present embodiment, taking the outermost peripheral cell as astarting cell, taking any cell of the third to the twentieth celllocated inwardly from the starting cell as an end cell and taking cellslocated inwardly from the end cell as basic cells, it is preferred thata relation between thickness (Tc) of partition walls forming the basiccells and each thickness (Tr1, Tr3-20) of partition walls forming thestarting cell and the end cell is 1.10≦(Tr1, Tr3-20)/Tc≦3.00. When thisvalue [(Tr1, Tr3-20)/Tc1 is less than 1.10, it does not contribute toimprove erosion resistance and isostatic strength. Therefore it does notcontribute to improve canning property. When the value is more than3.00, heat capacity and pressure loss are increased. Further, when thepartition wall thickness (Tr1, Tr2) of the first and the second cells ismade large at a particular proportion, there is no improvement inerosion resistance or isostatic strength. When even the wall thicknessof cells from first to over than twentieth cell, particularly to overthan thirtieth cell are made large at a particular proportion, pressureloss are increased and carrier mass are increased by more than required,resultantly heat capacity is increased. Therefore, it is not preferred.

In the present embodiment, it is also preferred for practicalapplication when heat capacity and pressure loss are taken intoconsideration that the relation between each partition wall thickness(Tr1, Tr3-20) and the basic cell wall thickness (Tc) is more restrictedso as to be 1.10≦(Tr1, Tr3-20)/Tc≦2.50, particularly 1.20≦(Tr1,Tr3-20)/Tc≦1.60.

The ceramic honeycomb structure according to the present embodiment ismade of at least one kind of ceramic selected from the group consistingof cordierite, alumina, mullite, silicon nitride, aluminum titanate,zirconia and silicon carbide, for example.

As the sectional shape of the ceramic honeycomb structure perpendicularto the channel in the present embodiment, there can be mentioned, forexample, a circle, an ellipse, an oval, a trapezoid, a triangle, atetragon, a hexagon or an asymmetry. Of these, a circle, an ellipse oran oval is preferred.

As a sectional shape of the cells perpendicular to the fluid channel inthe ceramic honeycomb structure of the present embodiment, polygonalshapes having three or more vertexes, such as square, rectangle orhexagon can be exemplified. Of these, a triangle, a tetragon or ahexagon is preferred.

As to the application of the ceramic honeycomb structure of the presentembodiment, there is no particular restriction. The honeycomb structurecan be used in various applications such as various filters, a catalystcarrier and the like. The ceramic honeycomb structure is preferably usedparticularly for a carrier for purification of automobile exhaust gas.Also, the ceramic honeycomb structure of the present embodiment ispreferably used by being accommodated in a catalytic converter case asshown in FIG. 7. In the Figure, the ceramic honeycomb structure 13 isaccommodated in a converter case 11 by being held with the ring 12 atthe outer surface. There is no particular restriction as to a materialof the ring 12. A metallic mesh-made ring is used ordinarily. Betweenthe converter case 11 and the outer surface of the ceramic honeycombstructure 13, a holding member 14 such as mat, cloth or the like isinterposed preferably.

Next, description is made on an embodiment of the process for producingthe ceramic honeycomb structure of the present invention. The method ofproducing the ceramic honeycomb structure of the present inventioncomprises the steps of obtaining a base material which is a unfired drybody of honeycomb structure having a plurality of partition walls usinga kneaded compound based on a ceramic material, adhering a partitionwall reinforcing agent to a part of partition wall located at least oneof the opening ends of the cells in the base material, and firing theresultant base material, wherein as the partition wall reinforcingagent, a material based on a compound having at least one kind of atomselected from the group consisting of Si, Ti, Mg and Al in its structureis used.

In the present embodiment, since firing of the base material (normalpartition wall part) and formation of the reinforced partition wall partcan be simultaneously conducted, it is possible to improve theproductivity and greatly reduce the product cost. Additionally, sincethe hydrophobic compound is used as the partition wall reinforcingagent, the water-soluble organic binder will not dissolve and swell whenthe partition wall reinforcing agent adheres to the partition walls, sothat a ceramic honeycomb structure having desired performance can beobtained without causing deformation of the partition walls such as celltwisting.

Furthermore, in the present embodiment, since a compound having in itsstructure an atom contributing to reinforcement of partition wall isused as the partition wall reinforcing agent, the atom contributing toreinforcement of partition wall is usually located in a uniform mannerin its physiochemical property. For this reason, it is possible to forma uniform reinforced partition wall part without taking a specialmeasure such as dispersing, and to almost completely avoid an occurrenceof local erosion. Therefore, even when the mean porosity is uniformthroughout the reinforced partition wall part, it is possible to form areinforced partition wall part having better erosion resistance than theconventional ceramic honeycomb structure. Furthermore, by using theabove partition wall reinforcing agent, a product-to-product variationof erosion resistance is also eliminated. Therefore, it is possible toobtain a ceramic honeycomb structure having excellent erosion resistancemore stably by a easier process. In the following, concrete explanationwill be made for each step.

In the present embodiment, first a formed body of honeycomb structurehaving a plurality of partition walls is prepared using a kneadedcompound based on a ceramic material.

In the present embodiment, the ceramic material is not particularlylimited, and at least one selected from the group consisting of siliconcarbide, boron carbide, titanium carbide, zirconium carbide, siliconnitride, boron nitride, aluminum nitride, alumina, zirconia, mullite,cordierite forming raw material, aluminum titanate and sialon can beused. The relationship with the partition wall reinforcing agent will bedescribed later.

In the present embodiment, other additives may be contained in thekneaded compound as necessary. Examples of such additive includewater-soluble organic binders, crystal growth auxiliary agents,dispersing agents and pore-forming agents. Examples of the water-solubleorganic binders include hydroxypropylmethyl cellulose, methyl cellulose,hydroxyethyl cellulose, carboxylmethyl cellulose, polyvinyl alcohol andpolyvinyl acetal. Examples of the crystal growth auxiliary agentsinclude magnesia, silica, yttria and iron oxide, and examples of thedispersing agents include ethylene glycol, dextrin, fatty acid soap andpoly alcohols. Examples of the pore-forming agents include graphite,wheat flour, starch, phenol resin and polyethylene terephthalate. Theseadditives may be contained singly or in combination of two or more kindsdepending on the particular object.

In the present embodiment, since the hydrophobic compound is used as thepartition wall reinforcing agent as described above, the water-solubleorganic binder will not dissolve and swell when the partition wallreinforcing agent is adhered to the partition wall, so that deformationof partition wall such as cell twisting will not occur. Therefore, thepresent embodiment is desirably applied to the production method inwhich the water-soluble organic binder is contained in the kneadedcompound.

The kneaded compound may be prepared in a routine method, for example,by mixing a predetermined amount of water or the like into the ceramicmaterial into which an additive such as water-soluble organic binder hasbeen added, adding another additive as necessary, and kneading theresultant mixture using a kneader, pressure kneader or vacuum augermachine.

In the present embodiment, the method for obtaining a formed body ofhoneycomb structure (forming method) is not particularly restricted.However, from the view point of achieving excellent mass productivity,extrusion forming is preferred, and for example, extrusion forming usingan extruder such as ram extruder or twin-screw extruder is preferred.

In the present embodiment, also the thickness of partition wall of thebase material (wall thickness of normal partition wall part) is notparticularly restricted. For instance, even with the base materialhaving partition walls of 0.05 mm or less thick, a formed body having adesired honeycomb structure is obtained without causing deformation inthe partition walls. Then the obtained formed body is dried to obtain abase material which is a dry body having a honeycomb structure. Fordrying the formed body, any suitable drying methods can be employedinsofar as they will not substantially cause firing. Examples of thedrying methods include the blast drying, hot air drying and microwavedrying. In this context, “dry body” means an unfired dry body which isnot substantially fired.

In the present embodiment, then prior to firing, the partition wallreinforcing agent is adhered to the plurality of partition walls locatedat the opening ends of the cells of the resultant base material (drybody).

At this time, according to the present embodiment, those based on thecompounds having at least one atom in their structures, morespecifically at least one atom selected from the group consisting of Si,Ti, Mg and Al that makes the partition walls located at the ends moreclose-grained by lowering the melting point of the base material formingmaterial, or going into the fine pores in the partition walls to lowerthe volume of the fine pores are used as the partition wall reinforcingagent.

In the present embodiment, as the compound that is to be a basis of thepartition wall reinforcing agent, compounds that generate inorganicoxides upon firing are preferred.

As the compound having Ti or Al in its structure, for example, aluminatealkoxy oligomers such as acetoalkoxy aluminum diisopropylate or titanatealkoxy oligomers used as a coupling agent are preferably used.

As the compound having Si in its structure, compounds having a siloxanebond, for example, silicone oil, silicon varnish, silicate alkoxyoligomer, mixtures thereof and the like are preferred.

Examples of the silicone oil include dimethyl silicone oil, methylphenylsilicone oil, methyl hydrogen silicone oil, amino-modified silicone oil,epoxy-modified silicone oil, carboxyl-modified silicone oil,carbinol-modified silicone oil, methacryl-modified silicone oil,mercapto-modified silicone oil, phenol-modified silicone oil, one endreactive silicone oil, different functional group-modified silicone oil,polyether silicone oil, methylstylyl-modified silicone oil,alkyl-modified silicone oil or higher fatty acid ester-modified.

In the present embodiment, the partition wall reinforcing agent may beprepared from one compound or mixture of two or more kinds selected fromthe compounds as exemplified above. It is especially preferred toprepare the partition wall reinforcing agent by mixing two or morekinds. When the partition wall reinforcing agent is prepared by mixingtwo or more kinds of the aforementioned compounds, it is possible toselect and mix the above compounds having a variety of viscosities, andhence to adjust the viscosity of the partition wall reinforcing agent asdesired. This facilitates uniform adhesion of the partition wallreinforcing agent. Also by arbitrarily selecting and mixing the abovecompounds, it is possible to arbitrarily control the degree ofreinforcement of the partition walls while securing the desired thermalshock resistance. Therefore, it is possible to give desired corrosionresistance in accordance with the thickness of the partition wall or thelike.

To be more specific, it is preferred to use the partition wallreinforcing agent prepared by mixing silicate alkoxy oligomer or methylhydrogen silicon oil into dimethyl silicone oil, for example.

Furthermore, in such a partition wall reinforcing agent, the blendingratio of silicate alkoxy oligomer (SAO) or methyl hydrogen silicone oil(MHSO) to dimethyl silicone oil (DMSO) (SAO or MHSO/DMSO) is preferablyfrom 10/90 to 75/25 (mass/mass), more preferably from 15/85 to 50/50(mass/mass), and more preferably from 20/80 to 50/50 (mass/mass),especially preferably from 25/75 to 50/50 (mass/mass). When the blendingratio falls within these ranges, it is possible to obtain a ceramichoneycomb structure having excellent erosion resistance while ensuringdesired thermal shock resistance.

Also, the partition wall reinforcing agent in the present embodiment maybe the aforementioned compounds such as silicone oil, that are dilutedin a diluent containing one or more than one selected from aromatichydrocarbons such as toluene or xylene, aliphatic hydrocarbons such aspetroleum ether or kerosene, petroleum-based hydrocarbons such as coaloil or diesel oil, alcohols such as isopropyl alcohol, lauryl alcohol orbutanol, volatile silicone oils and so on. Addition of such a diluentmakes it possible to arbitrarily control the degree of reinforcement ofpartition walls as well as to arbitrarily adjust the viscosity of thepartition wall reinforcing agent, so that uniform adhesion of thepartition wall reinforcing agent is achieved more easily.

In the present embodiment, the partition wall reinforcing agent has anabsolute viscosity of preferably from 1 to 10000 mPa·s, and morepreferably from 10 to 1000 mPa·s.

In general, a compound having low viscosity is small in degree ofpolymerization and tends to volatilize easily. If the viscosity is lessthan 1 mPa·s, when the compound adhered to the partition walls is fired,Si or the like active ingredient existing in the partition wallreinforcing agent volatilizes together with CO₂ and H₂O, so that itbecomes difficult to form a rigid reinforced partition wall part. To thecontrary, if the viscosity is more than 10000 mPa·s, the partition wallreinforcing agent is difficult to be adhered to the partition walls atuniform thickness.

Furthermore, preferably, the partition wall reinforcing agent in thepresent embodiment is suitably selected for each kind of ceramicmaterial. For example, in the case of a kneaded compound based on acordierite forming raw material, compounds having Si in their structuressuch as silicon oil are preferably selected.

In the present embodiment, when the partition wall reinforcing agent isadhered to the partition walls, by dipping the base material in thepartition wall reinforcing agent from the end face of the opening end ofthe cells to a predetermine height, it is possible to readily anduniformly adhere the partition wall reinforcing agent to all thepartition walls. This procedure is ideal in that the region where thereinforced partition wall part is to be provided can be easily andarbitrarily controlled. In order to adhere the partition wallreinforcing agent uniformly, however, it is preferred to remove thepartition wall reinforcing agent having excessively adhered after thedipping by compressive air or the like. Spray application can also beused for achieving uniform application of the partition wall reinforcingagent, however, with the spray application, it is difficult toarbitrarily control the region where the reinforced partition wall partis to be provided.

Next, in the present embodiment, the base material to which thepartition wall reinforcing agent has adhered is subjected to at leastone firing to simultaneously conduct firing (formation) of the normalpartition wall part and firing (formation) of the reinforced partitionwall part.

In the present embodiment, it is preferred to dry the base material andthe partition wall reinforcing agent in advance of the firing step, andexamples of the drying method include blast drying, hot air drying andmicrowave drying.

As for the firing condition, it is preferred to arbitrarily select adesired condition depending on the kinds of the base material and thepartition wall reinforcing agent. For example, in the case where thebase material is based on a cordierite forming raw material and thepartition wall reinforcing agent is based on a compound having Si in itsstructure such as silicone oil, the firing may be conducted at 1300 to1500° C.

In the above description, the production method according to the presentembodiment was explained step by step. With the production method of thepresent embodiment, it is possible to produce a ceramic honeycombstructure having excellent erosion resistance stably by a single firingstep without causing deformation or the like in the partition walls,while achieving high productivity and great reduction of the productcost.

The present invention is described more specifically below by way ofExamples. However, the present invention is in no way restricted bythese Examples.

EXAMPLE 1

To 100 parts by mass of a ceramic material comprising a cordieriteforming raw material, 8 parts by mass of methylcellulose, 0.5 part bymass of potassium laurate soap, 2 parts by mass of polyether and 28parts by mass of water were mixed, and the resultant mixture was loadedto a continuous extruder to obtain a formed body having a honeycombstructure. This formed body was dried to obtain a base material (unfireddry body) having a honeycomb structure.

Then the obtained base material was dipped in a partition wallreinforcing agent comprising dimethyl silicone oil (manufactured byShin-Etsu Chemical Co., Ltd. under the trade name of KF96-100CS,absolute viscosity: about 100 mPa·s) at a depth of 5 mm in the axialdirection from the opening end of the cells, to allow partition wallreinforcing agent to adhere the partition walls located at the openingend of the cells of the base material. Immediately after that,compressed air at room temperature was fed to remove the partition wallreinforcing agent that was adhered in excess.

Next, the base material having a honeycomb structure bearing thepartition wall reinforcing agent adhered to the partition walls locatedat the opening end of the cells was fired at 1400° C. for four hours toproduce a cylindrical ceramic honeycomb structure (not bearing catalyst)having a partition wall thickness of 0.064 mm, diameter of 100 mm andheight of 100 mm with square cells in the density of 140 cells/cm², andhaving a porosity of 85.5%. The porosity of the normal partition wallpart of the produced ceramic honeycomb structure was from 27 to 28%.

EXAMPLES 2 TO 4

A ceramic honeycomb structure was prepared in the same manner asdescribed in Example 1 except that as the partition wall reinforcingagent, methyl hydrogen silicone oil (manufactured by Shin-Etsu ChemicalCo., Ltd. under the trade name of KF99, absolute viscosity: about 20mPa·s) and dimethyl silicone oil (manufactured by Shin-Etsu ChemicalCo., Ltd. under the trade name of KF96L-0.65CS, absolute viscosity:about 0.65 mPa·s) blended in the ratios (mass/mass) of 10/90, 25/75 and50/50 were respectively used.

EXAMPLES 5 TO 7

A ceramic honeycomb structure was prepared in the same manner asdescribed in Example 1 except that as the partition wall reinforcingagent, silicate alkoxy oligomer (manufactured by Shin-Etsu Chemical Co.,Ltd. under the trade name of KR-500, absolute viscosity: about 20 mPa·s)and dimethyl silicone oil (manufactured by Shin-Etsu Chemical Co., Ltd.under the trade name of KF96L-0.65CS, absolute viscosity: about 0.65mPa·s) blended in the ratios (mass/mass) of 10/90, 25/75 and 50/50 wererespectively used.

EXAMPLES 8 TO 10

A ceramic honeycomb structure was prepared in the same manner asdescribed in Example 1 except that as the partition wall reinforcingagent, methyl hydrogen silicone oil (manufactured by Shin-Etsu ChemicalCo., Ltd. under the trade name of KF99, absolute viscosity: about 20mPa·s) and dimethyl silicone oil (manufactured by Shin-Etsu ChemicalCo., Ltd. under the trade name of KF96L-1000CS, absolute viscosity:about 1000 mPa·s) blended in the ratios (mass/mass) of 10/90, 25/75 and50/50 were respectively used.

EXAMPLE 11

A ceramic honeycomb structure was prepared in the same manner asdescribed in Example 1 except that as the partition wall reinforcingagent, methyl hydrogen silicone oil (manufactured by Shin-Etsu ChemicalCo., Ltd. under the trade name of KF99, absolute viscosity: about 20mPa·s) and coal oil (manufactured by Nisseki Mitsubishi Co., Ltd.)blended in the ratio (mass ratio) of 25/75 were used.

COMPARATIVE EXAMPLE 1

A honeycomb structure was prepared in the same manner as described inExample 1 except that a partition wall reinforcing agent is not adheredto the base material having a honeycomb structure.

COMPARATIVE EXAMPLE 2

A ceramic honeycomb structure was prepared in the same manner asdescribed in Example 1 except that as the partition wall reinforcingagent was used a dispersion prepared by adding 0.5 parts by mass ofdispersing agent (alkyl acetalized polyvinyl alcohol, manufactured bySEKISUI CHEMICAL CO., LTD. under the trade name of S-LEC KW-3) to 100parts by mass of a dispersion of 5% by mass of silica (SiO₂) powder inwater serving as a dispersing medium.

COMPARATIVE EXAMPLE 3

A ceramic honeycomb structure was prepared in the same manner asdescribed in Example 1 except that as the partition wall reinforcingagent was used a dispersion prepared by adding 0.5 parts by mass ofdispersing agent (polyoxyalkylene group polymer, manufactured by NOFCORPORATION under the trade name of MALIALIM AKM-0531) to 100 parts bymass of a dispersion of 5% by mass of silica (SiO₂) powder inpetroleum-based hydrocarbon (manufactured by Nisseki Mitsubishi Co.,Ltd., coal oil/CRISEF oil (trade name) F8 mixture, main component: coaloil) serving as a dispersing medium.

The ceramic honeycomb structure obtained in each of Examples andComparative Examples was examined for porosity, erosion resistance,isostatic strength and thermal shock resistance in the manner asdescribed below.

1. Porosity 1 (Product-to-Product Difference)

In five ceramic honeycomb structural bodies obtained in each of Examplesand Comparative Examples, as shown in FIG. 1, a measuring sample 6 wascut out in an area of 70 cm² which is almost the whole area of the endface in the reinforced partition wall part, and porosity of eachmeasuring sample was measured, and the maximum difference was determinedin the manner as described below.

2. Porosity 2 (Uniformity of Reinforced Partition Wall Part)

To examine whether the erosion resistance is uniform throughout thereinforced partition wall part, as shown in FIG. 2, for the reinforcedpartition wall part of one ceramic honeycomb structure obtained in eachof Examples and Comparative Examples, measuring samples 7 having an areaof 9 cm² were cut out at the total of five regions including one centerregion and four peripheral regions in the end face, and porosity of eachmeasuring sample was measured, and the maximum difference was determinedin the manner as described below.

3. Measurement of Porosity

-   -   (1) The sample was dried at 150 degree C. for 2 hours and placed        in a container. The container was set in a tester.    -   (2) Mercury was injected into the container. A pressure        corresponding to a predetermined pore diameter was applied. The        volume of mercury absorbed by the sample was measured.    -   (3) Pore distribution was calculated from the applied pressure        and the volume of mercury absorbed.    -   (4) Pore volume was calculated from the volume of mercury        absorbed by applying a pressure of 68.6 MPa (700 kgf/cm2).    -   (5) Porosity was determined from a total pore volume using the        following formula.        Porosity (%)=total pore volume (per g)×00/(total pore volume        (per g)+1/2.52]        4. Erosion Resistance

A metallic can holding and accommodating a ceramic honeycomb structurewas connected to the exhaust port of a gasoline engine of in-line fourcylinders and 1.8 liters displacement. That is, a sample was placedright near the engine. Next, the engine was operated under theconditions shown in FIG. 8 and, when the engine revolutions reached6,000 rpm, 0.1 g of abrasive grains (silicon carbide, GC 320, averageparticle diameter: 50 im) were added. Further, the engine operation wascontinued under the conditions shown in FIG. 8; once in each two cycles(one cycle: 130 seconds), abrasive grains were added; this was repeatedcontinuously. Test was conducted several times by changing the totalamount of abrasive grains added between about 2 g and 16 g, and from theresults was calculated the erosion amount (wind erosion volume) of theceramic honeycomb structure when the amount of abrasive grains added was10 g.

Erosion amount was measured by, as shown in FIG. 9, winding a rubbersheet round the end face of a ceramic honeycomb structure 1 whoseerosion amount was to be measured, placing therein ceramic-made beads of1.5 mm in diameter at a height of about 3 mm, then recovering them tomeasure the volume of beads, and calculating a difference between beadsvolume after erosion test and beads volume before the test. This wasconducted three times and an average thereof was taken as erosionamount. Evaluation was made on three ceramic honeycomb structural bodiesobtained in each of Examples and Comparative Examples. When the erosionamount exceeds 3 cc in all the three samples, the symbol “X” was givenrepresenting unendurability to practical use. When both the erosionamount of 2 cc or less and the erosion amount exceeding 3 cc areobserved, the symbol “Δ” was given; when all of the erosion amounts fallwithin the range of 2 to 3 cc, the symbol “◯” was given; and when all ofthe erosion amounts are less than 2 cc, the symbol “⊚” was given.

5. Isostatic Strength

A test based on an automobile standard JASO M 505-87 was conducted tomeasure a value of applied pressure when breakage occurs. The valuerepresents isostatic strength (kg/cm²).

6. Thermal Shock Resistance

After heating the ceramic honeycomb structure to a predeterminedtemperature in an electric furnace, the ceramic honeycomb structure wastaken out and placed in room temperature atmosphere of 20° C., andwhether defects such as cracking occurred due to thermal shock werevisually checked both in the elevated temperature condition immediatelyafter taking out the ceramic honeycomb structure, and in the conditionafter cooling by cold air (the condition at 20° C.). When no defect wasobserved, the heating temperature was further elevated, and the test wasrepeated until some defect occurred. The temperature at which the defectoccurred was determined to evaluate the thermal shock resistance.

(Evaluation)

In the production method according to Comparative Example 1 in which nopartition wall reinforcing agent is used, all of the five obtainedceramic honeycomb structural bodies have large porosity of 27 to 28%,which demonstrated that the ceramic honeycomb structure is unendurableto practical use in respect of the erosion resistance.

In the production method according to Comparative Example 2 in which adispersion of silica (SiO₂) powder in water was used as the partitionwall reinforcing agent, as shown in FIG. 4, significant deformation thatis visible to the naked eye was observed in the partition walls of theobtained ceramic honeycomb structure, and any of the obtained fiveceramic honeycomb structural bodies showed an isostatic strength of assmall as 3 to 5 kg/cm², which is unendurable to practical use. Inaddition, the maximum difference in mean porosity in the reinforcedpartition wall part among the five ceramic honeycomb structural bodieswas 5%. Also the erosion resistances largely varied among the productsin the range of 1.2 to 3.2 cc. Taking one ceramic honeycomb structure,the maximum difference in porosity was as large as 5%, so that a localerosion phenomenon is more likely to occur compared to the ceramichoneycomb structure obtained in Example as will be described later. Thissuggests that when the mean porosity is uniform throughout thereinforced partition wall part, the erosion resistance is smaller.

Likewise, in the production method according to Comparative Example 3 inwhich a dispersion of silica (SiO₂) in a petroleum-based hydrocarbon isused as the partition wall reinforcing agent, the maximum difference inmean porosity of the entire reinforced partition wall part among theobtained five ceramic honeycomb structural bodies was 8%, and theerosion resistance more largely varied among the products in the rangeof 1.1 to 3.5 cc. The maximum difference in porosity in one ceramichoneycomb structure increased to 7%, suggesting that a local erosionphenomenon is more likely to occur in the reinforced partition wallpart.

To the contrary, in the production methods according to Examples inwhich the partition wall reinforcing agent comprising a compound havingSi in its structure is adhered to the partition wall, as shown in FIG. 3(FIG. 3 shows a ceramic honeycomb structure obtained in Example 1), nodeformation was observed in the partition walls, and isostatic strengthof not less than 21 kg/cm² which is completely acceptable to practicaluse was achieved. Furthermore, the entire reinforced partition wall parthad a mean porosity in the range of 14 to 24%, which is lower by 3 to13% than that of the unreinforced part, suggesting that erosionresistance is increased. It was also confirmed that the maximumdifference in mean porosity of the entire reinforced partition wall partamong the five ceramic honeycomb structural bodies was 1%, representingvery small variation, and that the erosion resistance was not more than3 cc in every case. Also in one ceramic honeycomb structure, thereinforced partition wall part was uniformly formed as is apparent fromthe maximum difference in porosity of not more than 1%. This suggeststhat a local erosion phenomenon is not likely to occur in the reinforcedpartition wall part, and the erosion resistance is improved in theentire reinforced partition wall part.

In the production methods according to Examples 2 to 4 and Examples 8 to10 in which a partition wall reinforcing agent prepared by mixing methylhydrogen silicone oil and dimethyl silicone oil was adhered to thepartition walls, the production methods according to Examples 5 to 7 inwhich a partition wall reinforcing agent prepared by mixing silicatealkoxy oligomer and dimethyl silicone oil was adhered to the partitionwalls, and the production method according to Example 11 in which apartition wall reinforcing agent prepared by mixing methyl hydrogensilicone oil and coal oil was adhered to the partition walls, it wasfound the mean porosity of the entire reinforced partition wall parttends to decrease as the content of methyl hydrogen silicone oil orsilicate alkoxy oligomer increases.

More specifically, in the ceramic honeycomb structural bodies obtainedin Examples 3, 4, 6, 7 and 9-11 in which the content of methyl hydrogensilicone oil or silicate alkoxy oligomer was 25% or more, a reinforcedpartition wall part having a mean porosity of not more than 21% wasobtained, and a very large erosion resistance was realized partlybecause of the effect of having uniform porosity. Furthermore, in theceramic honeycomb structural bodies obtained in Examples 4, 7 and 10 inwhich the content of methyl hydrogen silicone oil or silicate alkoxyoligomer was 50%, the reinforced partition wall part had a mean porosityof 14-15%, 16-17% and 14-15%, respectively, and erosion resistance wasstill larger. It should be noted that in any of Examples and ComparativeExamples, the obtained ceramic honeycomb structure exhibited a thermalshock resistance temperature of 700° C. or higher, which is practicallysufficient thermal shock resistance. Table 1 shows the used partitionwall reinforcing agents and the evaluation results. TABLE 1 Porosity ofreinforced partition wall part (%) Thermal shock Blending IsostaticProduct-to-product Uniformity of reinforced resistance Partition wallratio strength Erosion difference (n5) partition wall part (n1) (Limitreinforcing (mass/ (kg/cm²) resistance (Mean porosity of reinforced(Between center part and temperature agent mass) (n5) (n3) partitionwall part) peripheral parts) (° C.)) Example 1 DMSO*¹ 100 23˜25 ◯(2.4˜2.7 CC) 1%(23˜24) 1%(23˜24) 800 Example 2 MHSO*²/DMSO 10/90 21˜24 ◯(2.1˜2.5 CC) 1%(22˜23) 1%(22˜23) 800 Example 3 MHSO/DMSO 25/75 22˜25 ⊚(1.0˜1.3 CC) 1%(18˜19) 0%(19˜19) 750 Example 4 MHSO/DMSO 50/50 24˜27 ⊚(0.4˜0.6 CC) 1%(14˜15) 1%(14˜15) 700 Example 5 SAO*³/DMSO 10/90 25˜26 ◯(2.4˜2.8 CC) 1%(23˜24) 0%(23˜23) 800 Example 6 SAO/DMSO 25/75 22˜26 ⊚(1.5˜1.9 CC) 1%(20˜21) 0%(20˜20) 750 Example 7 SAO/DMSO 50/50 21˜25 ⊚(0.5˜0.9 CC) 1%(16˜17) 1%(16˜17) 750 Example 8 MHSO/DMSO 10/90 23˜25 ◯(2.1˜2.3 CC) 1%(21˜22) 0%(21˜21) 800 Example 9 MHSO/DMSO 25/75 23˜25 ⊚(1.0˜1.5 CC) 1%(18˜19) 0%(19˜19) 800 Example 10 MHSO/DMSO 50/50 21˜26 ⊚(0.6˜0.9 CC) 1%(14˜15) 0%(15˜15) 750 Example 11 MHSO/COAL 25/75 21˜22 ⊚(1.2˜1.9 CC) 1%(19˜20) 1%(19˜20) 750 OIL Comparative — — 21˜25 X(4.0˜4.7 CC) 1%(27˜28) 0%(27˜27) 800 Example 1 Comparative SiO₂powder/H₂O  5/95 3˜5 Δ (1.2˜3.2 CC) 5%(20˜25) 5%(21˜26) 750 Example 2Comparative SiO₂ powder/HC  5/95 21˜25 Δ (1.1˜3.5 CC) 8%(18˜26)7%(17˜24) 750 Example 3*¹DMSO: Dimethyl silicone oil*²MHSO: Methyl hydrogen silicone oil*³SAO: Silicate alkoxy oligomer

Industrial Applicability

As explained above, according to the present invention, it is possibleto obtain a honeycomb structure having desired performance withoutcausing any deformation or the like in partition walls whiledramatically improving the productivity and achieving cost reduction.

Additionally, it is possible to accurately form a sophisticated anduniform reinforced partition wall part, and to stably obtain a ceramichoneycomb structure having excellent erosion resistance. Of course, theobtained ceramic honeycomb structure has greatly uniformed porositythroughout the reinforced partition wall part, and hence has moreexcellent erosion resistance because local erosion phenomenon is avoidedalmost completely.

1-20. (canceled)
 21. A ceramic honeycomb structure comprising: a cell group having cells, the cells being divided each other by porous partition walls and functioning as a fluid channel; and a porous outer wall surrounding and holding outermost peripheral cells located at a circumference of the cell group, characterized in that in the partition walls, a part located at least one opening end of the cells of the cell group constitutes a reinforced partition wall part having higher strength than the other part of the partition walls (normal partition wall part) as well as having a variation of porosity per unit volume within ±2%.
 22. The ceramic honeycomb structure according to claim 21, wherein the value of porosity (%) of the reinforced partition wall part is smaller than the value of porosity (%) of the normal partition wall part by 3(%) or more.
 23. The ceramic honeycomb structure according to claim 21, wherein porosity of the reinforced partition wall is 30% or less.
 24. The ceramic honeycomb structure according to claim 21, wherein the minimum partition wall thickness of the partition walls is in the range of 0.030 to 0.076 mm.
 25. The ceramic honeycomb structure according to claim 21, wherein the length of the reinforced partition wall part from the end face of the opening end of the cells to a tip end thereof is not uniform throughout the reinforced partition wall part.
 26. The ceramic honeycomb structure according to claim 21, wherein the partition wall thickness of the reinforced partition wall part is larger than the partition wall thickness of the normal partition wall part.
 27. The ceramic honeycomb structure according to claim 21, wherein taking the outermost peripheral cell as a starting cell, taking any cell of the third to the twentieth cell located inwardly from the starting cell as an end cell and taking cells located inwardly from the end cell as basic cells, a relation between thickness (Tc) of partition walls forming the basic cells and each thickness (Tr1, Tr3-20) of partition walls forming the starting cell and the end cell is 1.10≦(Tr1, Tr3-20)/Tc≦3.00.
 28. The ceramic honeycomb structure according to claim 21, comprising at least one kind of ceramic selected from the group consisting of cordierite, alumina, mullite, silicon nitride, aluminum titanate, zirconia and silicon carbide.
 29. The ceramic honeycomb structure according to claim 21, wherein a sectional shape of the honeycomb structure perpendicular to the channel is circular, elliptic, oval, trapezoidal, triangular, tetragonal, hexagonal or asymmetric.
 30. The ceramic honeycomb structure according to claim 21, wherein the sectional shape of the honeycomb structure perpendicular to the channel is triangular, tetragonal or hexagonal.
 31. The ceramic honeycomb structure according to claim 21, used as a carrier of catalyst for automobile exhaust gas emission control.
 32. The ceramic honeycomb structure according to claim 21, incorporated into a catalyst converter in such a manner that the partition walls bear a catalyst component and the ceramic honeycomb structure is held at the outer circumference of the outer wall.
 33. A method of producing a ceramic honeycomb structure comprising the steps of: obtaining a base material which is a dry body having a honeycomb structure with a plurality of partition walls by using a kneaded compound based on a ceramic material; adhering a partition wall reinforcing agent to a part located at at least one of the opening ends of the cells of the base material; and firing the base material; characterized in that as the partition wall reinforcing agent, the one that is based on a compound having in its structure at least one atom selected from the group consisting of Si, Ti, Mg and Al is used.
 34. The method of producing a ceramic honeycomb structure according to claim 23, wherein the basis of the partition wall reinforcing agent is a compound that generates an inorganic oxide upon firing.
 35. The method of producing a ceramic honeycomb structure according to claim 23, wherein the basis of the partition wall reinforcing agent is a compound that has a siloxane bond.
 36. The method of producing a ceramic honeycomb structure according to claim 23, wherein the basis of the partition wall reinforcing agent is silicone oil, silicone varnish, alkoxy oligomer or mixture thereof.
 37. The method of producing a ceramic honeycomb structure according to claim 33, wherein absolute viscosity of the partition wall reinforcing agent is in the range of 1 to 10000 mPa·s.
 38. The method of producing a ceramic honeycomb structure according to claim 33, wherein the ceramic material is a cordierite forming raw material.
 39. The method of producing a ceramic honeycomb structure according to claim 33, wherein the kneaded compound contains a water-soluble organic binder.
 40. The method of producing a ceramic honeycomb structure according to claim 39, wherein the water-soluble organic binder comprises at least one kind of water-soluble compound selected from the group consisting of hydroxypropylmethyl cellulose, methylcellulose, hydroxyethyl cellulose, carboxylmethyl cellulose, polyvinyl alcohol and polyvinyl acetal. 